When using the Form Editor or Main Window Editor, there is a toggle button Show Errors in the ribbon.

When enabled, any object that is in an error or warning state, for example, a missing source for an input field object, will show an icon in the corner of that object. In addition, a similar error or warning icon will be shown in the application tree. This makes it easy to locate errors in a form or main window design. By default, the Show Errors button is disabled.